The present invention relates to an image reading device installed in a copier, facsimile apparatus or similar image forming apparatus and, more particularly, to a device for reading the images of a book document and having a page turning capability.
An automatic document feeder (ADF) is extensively used with an image forming apparatus of the kind described as an image reading device. The ADF automatically transports a sheet document to a reading position, reads the image of the document, and then discharges the document from the reading device. So far as the document is a sheet document, the ADF can read it automatically. However, regarding a book document, it is extremely difficult to automate the page turning operation of the ADF. The only measure left at the present stage of development is to turn the pages of a book manually. Although various methods and means have, of course, been proposed for reading a book document automatically, most of them are merely conceptual and far from practicality.
In the light of this, Japanese Patent Laid-Open publication (Kokai) 5-19563 corresponding to Japanese Patent Application No. No. 2-193589 discloses a device capable of reading a book document while turning the pages thereof with a page turning and reading unit, or scanning unit as referred to hereinafter. The scanning unit has thereinside page receiving means, page attracting means, page separating means, reading means, etc. Specifically, the scanning unit has a page turning belt extending along the surface of a document table. While a document is laid on the document table in a spread position between the surface of the table and the belt, the scanning unit is moved relative to the document while causing the belt to form a roundabout portion moving away from the table. With this kind of device, it is possible to fully automate the page turning and image reading operation which has heretofore been time and labor consuming and, therefore, to implement a multifunction image reading system remarkably enhancing the productivity of, for example, a copier.
However, in the device described above, the right and left parts of a book spread on the document table are simply laid flat in the same plane. This brings about a problem that when the surfaces of the right and left parts of the spread book are different in height, the scanning surface of the document has a stepped portion and causes the scanning unit to move up and down at such a portion. As a result, both the image reading operation and the page turning operation of the scanning unit are unstable. Therefore, to stabilize such operations, it is preferable that the surfaces of the right and left parts of the spread book be positioned in the same flat plane.
For positioning the surfaces of the right and left parts of the spread book in the same flat plane, Japanese Patent Laid-Open Publication No. 61-184527, for example, teaches a see-saw type document supporting device. This type of device has a single flat glass plate and presses the right and left surfaces of the spread book against the glass plate from below. However, the problem with this device is that the glass plate intervening between the scanning unit and the book prevents the pages of the book from being automatically turned over, although only the spread pages may be read. Moreover, the see-saw type device relies on manual operation in pressing the book against the glass plate, it is difficult to exert an adequate pressure against the document surface stably. For these reasons, this type of device is not feasible for a unit scanning type apparatus intended for a fully automatic image reading and page turning procedure.
The right and left parts of the spread book may be laid on a right and a left document table, respectively, and pressed against the scanning unit from below independently of each other. This approach, however, has a drawback that the right or left part of the document not being read by the scanning unit is not restricted in elevation and, therefore, causes the associated table to rise more than necessary. This causes an inclination or a step to occur on the spread document.
Further, when the spread document is received by the scanning unit, as stated above, the resistance of the scanning unit acting on a unit support section when the unit is pressed increases, reducing the scanning ability. In this case, therefore, it is necessary to support the scanning unit such that the resistance decreases. In addition, in such a condition, the resistance of the scanning unit acting on the document when the unit is pressed increases. This, coupled with the fact that the ability of the scanning unit to follow the undulations of the spread book is lowered, aggravates the fall of scanning ability. Hence, it is also necessary to reduce the resistance of the scanning unit acting on the document.
Another drawback with the previously stated see-saw type document supporting device is that the manual document pressing arrangement increases the overall size of the device and renders the image reading or page turning operation of the scanning unit unstable.